Iris imaging telephone security module and method

ABSTRACT

A compact, handheld imaging apparatus which can be used to capture high-quality iris images for identification of a person. The handheld iris imager is non-invasive and non-contacting and comprises a camera, a cold mirror, a lens, and an illuminator. The imager has sensors and indicators which assist a user in aligning and focusing the device. The imager also automatically captures the image when proper positioning is achieved. A template of the image is then compared to a database of previously stored templates of images to identify the person. The imager is integrated into a telephone as a security module. The telephone cannot be unlocked and used unless a user has been identified and authorized by the imager.

FIELD OF THE INVENTION

The present invention relates in general to identification of physicalcharacteristics of a human being or other animal. More particularly, thepresent invention relates to iris recognition.

BACKGROUND OF THE INVENTION

Various technologies are used for uniquely identifying a person inaccordance with an examination of particular attributes of either theperson's interior or exterior eye. One of these technologies involvesthe visual examination of the particular attributes of the exterior ofthe iris of at least one of the person's eyes. The iris of the human eyehas random patterns of striations, ciliary processes, crypts, rings,furrows and other features which had been shown capable of generatinghighly unique biometric templates for personal identification. In thisregard, reference is made to U.S. Pat. No. 4,641,349, “Iris RecognitionSystem”, issued to Flom et al., and U.S. Pat. No. 5,291,560, “BiometricPersonal Identification System Based on Iris Analysis”, issued toDaugman. As made clear by these patents, the visible texture of aperson's iris can be used to distinguish one person from another withgreat accuracy. Thus, iris recognition can be used for such purposes ascontrolling access to a secure facility or a bank automatic tellermachine, for example. An iris recognition system involves the use of animager to video image the iris of each person attempting access, andimage processing means for comparing this iris video image with areference iris image on file in a database.

Iris identification systems have been developed that are capable ofcollecting images of the iris and processing them to produce biometrictemplates. These templates may be used to identify individual iriseswith extremely low error rates, on the order of 1 in 10⁷⁸. The systemscapture the iris images using stationary optical platforms that areoften large, complex, and expensive. The systems are difficult to usewith minimal cooperation of the subject being identified. As a resulttheir usefulness in many applications is limited.

The cellular telephone industry each year loses an estimated $650million to cellular fraud, principally due to cloning of cellulartelephones. Cloning involves re-programning a phone's electronic serialnumber and telephone number to those stolen from a legitimatesubscriber. To counteract cloning, some service providers have utilizedpersonal authentication techniques such as personal identificationnumbers (PIN) or voice verification to verify that the authorizedsubscriber is using the phone. This is unreliable because PIN number canbe stolen or forgotten, and voice verification messages may be recorded.

Although the art of human recognition systems is well developed, thereremain some problems inherent in this technology, particularly the lackof an iris imager and security module suitable for integration into acellular telephone, and the lack of a method for using biometricinformation for enabling access to the cellular network. Therefore, aneed exists for a recognition system that overcomes the drawbacks of theprior art.

SUMMARY OF THE INVENTION

The present invention is directed to a telephone security modulecomprising: iris acquisition means having a front surface for obtainingan image of an iris of an eye; a lens having a image plane disposed infront of the front surface of the iris acquisition means; a mirrordisposed on a side of the lens opposite the iris acquisition means; anilluminator disposed along a side of the mirror; a memory for storing aniris image obtained by the iris acquisition means; a processor forextracting a template from the stored iris image; and a communicationsinterface for transmitting the template to a central station.

According to one aspect of the invention, the iris acquisition meanscomprises a camera, and the mirror is a cold mirror. The camera issensitive to light having a wavelength in a range between about 400 nmand about 1100 nm. The mirror reflects light having a wavelength in arange between about 400 nm and about 700 nm and passes light having awavelength greater than about 700 nm.

According to another aspect of the present invention, the illuminatoremits light having a wavelength in a range between about 680 nm andabout 900 nm towards the iris of the eye being imaged, and the eye isout of contact with the iris imaging apparatus.

According to another aspect of the present invention, the module furthercomprises at least a visible indicator or an audible indicator toindicate when the image of the iris has been obtained. According toanother aspect of the present invention, the module further comprises afocus assessment processor coupled to the visible indicator and/or theaudible indicator.

According to another aspect of the present invention, the processorunlocks a telephone responsive to a signal received from the centralstation.

In a further embodiment within the scope of the present invention, amethod of unlocking a telephone responsive to the identification of aperson comprises the steps of: (a) storing image information of the irisof at least one person's eye; (b) illuminating an eye of an unidentifiedperson having an iris; (c) obtaining an image of the iris of theunidentified person; (d) determining if the image is an image ofsufficient quality for a step (f) of comparing; (e) repeating steps (b)through (d) until the image of sufficient quality is obtained; (f)comparing a template of the obtained image with the stored imageinformation to identify the unidentified person; and (g) unlocking thetelephone responsive to a result of the step of comparing. The storedimage information used for identification can be a code or templateextracted from the image, and the comparison can be performed at acentral database maintained by a telephone service provider.

According to one aspect of the present invention, the method furthercomprises the step of activating an indicator if the image is ofinsufficient quality. The indicator is an audible indicator.

According to another aspect of the present invention, the method furthercomprises the step of activating an indicator if the image is ofsufficient quality. The indicator is a visible indicator.

According to another aspect of the present invention, the method furthercomprises the step of activating an indicator responsive to the step ofcomparing. The indicator is a visible indicator.

In accordance with a further aspect of the present invention, the stepof determining if the image is an image of sufficient quality comprisesthe step of focus assessment processing the image.

According to another aspect of the present invention, the telephone isunlocked if the step of comparing identifies the person.

In a further embodiment within the scope of the present invention, asystem of identification of a person for unlocking a telephone comprisesa telephone security module, a second memory for storing at least onetemplate of at least one image of an iris of at least one person's eye;and a second processor for comparing the template of the stored irisimage with the at least one stored template of the second memory toidentify the person, and for unlocking the telephone responsive to theresult of the comparison.

In accordance with a further aspect of the present invention, the secondmemory and second processor are housed in a central station remote fromthe telephone security module.

In accordance with a further aspect of the present invention, the secondprocessor unlocks the telephone when the template of the stored irisimage substantially matches the at least one stored template of thesecond memory.

In a further embodiment within the scope of the present invention, atelephone security module comprises: iris acquisition means having afront surface for obtaining an image of an iris of an eye; a lens havinga image plane disposed in front of the front surface of the irisacquisition means; a mirror disposed on a side of the lens opposite theiris acquisition means; an illuminator disposed along a side of themirror; a first memory for storing at least one template of at least oneimage of an iris of at least one person's eye; a second memory forstoring an iris image obtained by the iris acquisition means; aprocessor for extracting a template from the stored iris image; and acomparator for comparing the template from stored iris image with the atleast one template to identify the person.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects of the present invention will becomeapparent from the following detailed description of the invention whenconsidered in conjunction with the accompanying drawings. For thepurpose of illustrating the invention, there is shown in the drawings anembodiment that is presently preferred, it being understood, however,that the invention is not limited to the specific methods andinstrumentalities disclosed. In the drawings:

FIG. 1 is a schematic diagram of an exemplary iris imager in accordancewith the present invention;

FIG. 2A is a schematic diagram of the imager of FIG. 1 shown in greaterdetail;

FIG. 2B is a schematic diagram of another exemplary imager in accordancewith the present invention;

FIG. 3 is a simplified flowchart of a method of operation in accordancewith the present invention;

FIG. 4 is a schematic diagram of an exemplary iris image recognitionsystem in accordance with the present invention;

FIG. 5 is a schematic diagram of an exemplary iris imager having visualand aural indicators in accordance with the present invention;

FIG. 6 is a more detailed flow chart of a method of operation inaccordance with the present invention;

FIG. 7 is a schematic diagram of an exemplary iris image recognitionsystem having a focus assessment processor in accordance with thepresent invention;

FIG. 8 is a schematic diagram of an exemplary iris imager incorporatedinto a telephone in accordance with the present invention;

FIG. 9 is an isometric view of an exemplary telecommunications irisimager and telephone in accordance with the present invention; and

FIG. 10 is a flow diagram of an exemplary method of operation of atelecommunications iris imager in accordance with the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS AND BEST MODE

The present invention is directed to a compact, handheld imagingapparatus and method which can be used to capture high-quality irisimages. Preferably, the imager has sensors and indicators which assistthe human operator in aligning and focusing the device. The imager alsoautomatically captures the image when proper positioning is achieved.Because it is small and compact, it is practical for integration into acellular telephone where it is used to authenticate telephonesubscribers and eliminate cellular telephone fraud. Throughout thefollowing detailed description similar reference numbers refer tosimilar elements in the figures of the drawings.

FIG. 1 illustrates a preferred embodiment of the handheld imager 100 inaccordance with the present invention. The exemplary handheld,non-invasive, non-contacting iris imager comprises iris acquisitionmeans 105, an imaging lens 110, a mirror 120, an optional dioptercorrection lens 125, and an illuminator 130. The imager 100 ispreferably powered by a standard DC supply provided by a cellulartelephone.

The iris acquisition means 105 is preferably a conventional solid statevideo camera, such as a charged coupled device (CCD) or complementarymetal oxide semiconductor (CMOS) device. A preferred camera is a ⅓ inchformat, monochrome CCD board camera, such as Computar Model EM200.Preferably, the video camera 105 is sensitive to light of wavelengths inthe range of about 400 nanometers to about 1100 nanometers, and ispositioned so that its front surface coincides with the image plane ofthe lens 110 in front of it. In the preferred embodiment, the objectplane of the lens is approximately 89 mm in front of the lens 110. Morepreferably, the lens 110 is an optical lens with approximately 14.2 mmfocal length.

The mirror 120, preferably a concave cold mirror having a radius ofcurvature preferably about 276 mm, is disposed on the side of the lens110 opposite the video camera 105 and creates a magnified virtual imageof the iris behind the mirror 120. In the preferred embodiment, themirror 120 reflects visible light with wavelengths in the range of about400 to about 700 nanometers, and passes light having longer wavelengths,such as those in the range of about 700 to about 900 nanometers.

The illuminator 130 is positioned just outside the edge of the coldmirror 120 and is used to illuminate the iris of the subject beingidentified. The preferred illuminator 130 emits light having wavelengthsof about 680 to about 900 nanometers. Preferably, the illuminator 130 isa miniature quartz halogen or krypton gas bulb operating atapproximately 1 watt.

The imager acquires images of an iris with sufficient clarity, focus,and size for use with conventional image processing and comparisonroutines, preferably in less than about 3 seconds. A preferred imageprocessing and comparison routine is described in U.S. Pat. No.5,291,560, “Biometric Personal Identification System Based on IrisAnalysis”, issued to Daugman, and commonly assigned with the presentinvention to IriScan Inc., and incorporated herein by reference.However, any processing and comparison technique can be used with theimage that is acquired at the imager, such as the image pixelcorrelation technique described in U.S. Pat. No. 5,572,596, “Automated,Non-Invasive Iris Recognition System and Method”, issued to Wildes etal. and the techniques described in U.S. Pat. No. 4,641,349, “IrisRecognition System”, issued to Flom et al., both of which areincorporated herein by reference.

FIG. 2A shows the apparatus of FIG. 1 in greater detail. The lens 110gives a high resolution image of the eye 150 of the user, who ispositioned in front of the lens 110, so that extreme proximity betweenthe eye 150 and the imager 100 is not required (i.e., no contact isneeded between the subject and the imager 100).

The handheld iris imager comprises a solid-state image capture deviceand an optical system which forms an image 109 of the iris on the imagecapture device at the image plane of the video camera 105 and at thesame time produces a virtual image 115 of the iris which the user canuse to position and focus the iris image. As a result, the user can,using the same eye being imaged, see a reflected image of the iris whichcan be used to position the handheld imager 100 so that a good irisimage (i.e., an image that can be processed and compared to those storedin a database) can be obtained.

FIG. 2A also shows an optional dioptric correction lens 125 positionedbetween the eye 150 and the cold mirror 120. The dioptric correctionlens 125 is an adjustable optical element which corrects for theclose-range focusing ability of the individual eye, which varies fromsubject to subject. When the lens 125 is properly adjusted, themagnified, reflected virtual image 115 of the subject's eye appears insharp focus to the subject at the same eye-to-mirror distance at whichthe subject's eye is sharply focused on the front surface of the camera.This simplifies use of the imager, because the subject simply positionsthe image so that the virtual image 115 of the iris appears sharplyfocused.

A preferred embodiment of the dioptric correction mechanism has nocorrection lens 125 and instead has a mechanical means (not shown) foradjusting the position of the cold mirror 120 relative to the cameralens 110. This allows the user to vary the object distance of the coldmirror 120, thus changing the eye-to-lens distance at which the virtualimage 115 of the iris is sharply focused.

The ability to set the dioptric correction mechanism to accommodate aparticular user has a great utility if the imager is used by only oneperson most of the time. Once the correction is set, the user can easilyposition the device to obtain a sharply focused reflected image. Thisautomatically produces a sharply focused image from the camera andsubstantially immediate acceptance of the image by the focus assessmentprocessor described below. Image capture time is thereby reduced andoverall convenience and utility is enhanced.

An eye 150 is positioned in front of the imager 100 (e.g., about 3.5inches in front), as shown in FIG. 2A, and the illuminator 130 is turnedon. This, in turn, illuminates the eye 150 and the iris therein.Preferably, the light having wavelengths of about 400 to about 700nanometers is reflected by the cold mirror 120, thereby forming amagnified virtual image 115 behind the mirror 120 which the user can seethrough the eye being imaged. The radius of curvature of the mirror isselected so that the magnified image 115 of the eye substantially fillsthe user's entire field of view. Hence, when the imager 100 ispositioned so that the entire eye 150 is visible, it is virtuallyassured that the eye 150 will be substantially centered in the objectplane 140 of the camera 105. Under these conditions, the light havingwavelengths of about 700 to about 900 nanometers is passed by the mirror120 and forms an approximately centered image 109 of the eye 150 at theimage plane 107 of the camera 105. The image is then captured andprocessed, as described below.

Although a cold mirror (one which reflects shorter wavelengths andpasses longer wavelengths) is described herein, it is understood that ahot mirror (one which reflects longer wavelengths and passes shorterwavelengths) could also be used in accordance with the presentinvention. Such a configuration is shown in an imager 101 in FIG. 2B.The eye 150 is illuminated by an illuminator 131 emitting light havingwavelengths in the range of about 680 to 900 nanometers. This light isreflected by the eye 150 and the light having wavelengths in the rangeof about 700 to 900 nanometers is reflected by the hot mirror 121 to befocused by the lens 111 onto the front surface of the camera 106. Lightreflected from the eye 150 having shorter (visible) wavelengths in therange of about 400 to 700 nanometers passes through the hot mirror 121and strikes a concave broadband mirror 122 which reflects light havingwavelength from about 400 to 900 nanometers. This light forms a virtualimage 115 of the eye 150 behind the concave mirror 122 that the user cansee and use to align and focus the device, as described below.

The imager 100 of FIGS. 1 and 2A, as well as the imager of FIG. 2B, isused in a system to identify the iris image that has been captured. Asshown in FIG. 3, the eye is illuminated at step 160, and an acceptableor suitable image of the iris is obtained at step 165. The image isprocessed to extract an iris template or code at step 170, the templateor code is encrypted (optional) and transmitted to the cellular provider(such as a central station; e.g., a Mobile Telephone Switching Office)at step 175, and the template or code is decrypted (if necessary) andcompared to pre-existing templates or codes of authorized subscribersstored in a memory or database for identification and authorization ofthe user at step 180. If the user is authorized, the cellular providerenables the call placement at step 185. The cellular provider can eitherenable the call at the central station or send a signal to the telephoneprocessor directing it to unlock the telephone.

FIG. 4 is a schematic diagram of an exemplary iris image recognitionsystem in accordance with the present invention. The imager 100 iscoupled to a microprocessor 210 that performs the processing andencryption. The microprocessor 210 resides in a cellular telephone 200.

The microprocessor 210 is coupled to the imager 100 via conventionalcables and/or printed circuit boards (PCBs) that are incorporated intothe telephone 200. Other conventional means for coupling the imager 100and the microprocessor 210 can be employed. The microprocessor 210controls the imager 100 and runs software held in read only memory (ROM)205. The processor 210 is connected via a bus 207 to the ROM 205, arandom access memory (RAM) 232, another memory such as an erasableprogrammable ROM (EPROM) 230, and an input/output (I/O) controller 225.The RAM 232 is large enough to hold at least one captured image of aniris. The I/O controller 225 is connected to the appropriate circuitryand drivers (not shown) for issuing commands to control the imager 100.

The imager 100 preferably uses a digital camera and transmits digitalimages directly to the processing unit 210. “On/off” data is transmittedfrom the imager 100 to the processor 210 to initiate the imageacquisition function. A digital image could be provided if a digitalcamera is used.

The image processing consists of a number of image processing steps(such as those described in U.S. Pat. No. 5,291,560 and U.S. Pat. No.5,572,596, which are herein incorporated by reference) which lead toextraction of a unique and highly specific digital biometric templatethat can be used to identify the individual based on intensity patternswithin the iris. The biometric template is transmitted to the cellularprovider where it is compared against other templates stored in a memoryor database. The database stores selected data representing images ofthe iris of a plurality of subjects. A match of the biometric templatewith a template stored in the database identifies the subject whose irisis being imaged.

Although an image of the eye is reflected back to the subject in mirror120, this may not provide the desired feedback to the user to enable theuser to properly position the imager so that a suitable iris image isobtained. For example, a user may be a novice in using and positioningthe imager 100 with respect to the eye 150, or the user may beattempting to image the eye of another subject with the imager. Thus,preferably, the imager 100 comprises a passive feedback mechanism toguide the user in positioning the eye 150 to an optimum location toallow acquisition of a suitable image.

The passive feedback mechanism is an indicator or combination ofindicators that provides, on a near real-time basis, an indication tothe user that an adequate iris image has or has not been obtained. FIG.5 is a schematic diagram of an exemplary iris image recognition systemthat includes position indicators in accordance with the presentinvention. Preferably, the indicator is visible and/or audible, such as,for example, an indicator lamp 305 (e.g., a light emitting diode (LED))that lights when an acceptable image has been captured (i.e., “imageacquired”), and a aural indicator via a speaker 310, such as a beep orother tone, that sounds periodically until an acceptable image has beencaptured (i.e., “imaging in progress”).

Additional indicators 306, 307 can be also be used, either alone or incombination, for such indications as “subject identified-accept” and“subject not identified-reject”. These indications would be activatedpursuant to the results of the processing and comparison performed atthe database server at the cellular provider, as described above withrespect to FIG. 3. Alternatively, other display devices, such as liquidcrystal displays used for other purposes within the telephone, could beused as indicators.

The imager 100 also preferably has an on/off switch (not shown), such asa pushbutton, for powering up the imager and initiating the imageacquisition process. Power for the imager 100 is preferably supplied bya battery. The imager 100 receives and acts on instructions from theprocessor 210 to perform functions such as lighting or turning off theindicator lamp(s) 305, providing the audible signals via the speaker310, and lighting the ‘accept’ and ‘reject’ indicators.

FIG. 6 is a more detailed flow chart of a method of operation inaccordance with the present invention. The eye is illuminated at step350 and an image of the iris is obtained at step 355. At step 360, it isdetermined if the image is suitable for use with the image processingand comparison routines. If the image is suitable, the image is passedto the processor for further processing, at step 370, and transmissionto the cellular provider. A comparison of the template to the templatesstored in a database at the cellular provider is performed at step 373.If the comparison provides a positive match, then authorization isgranted at step 376 for the user to use the phone. If the comparisondoes not provide a positive match, then authorization is not granted forthe user to use the phone.

If the image is not suitable at step 360, then at step 380, theindicator(s) is activated (e.g., a beep sound is issued), and processingcontinues at step 355 (i.e., another image is obtained).

Because the eye's own focusing system automatically adjusts to bring thevirtual image 115 into sharp focus to the user, it cannot be relied uponto always accurately focus the eye image on the camera 105. For thispurpose, a focus assessment system is used in one embodiment, as shownin FIG. 7. Digital video image information from the imaging device 100is stored in a frame buffer memory 410, such as a RAM similar to RAM 232described above with respect to FIG. 4, and capable of storing onecomplete frame of digitized video information. A focus assessmentprocessor 420 accesses the digitized image information and appliescertain measurement algorithms which are disclosed in a co-pendingapplication entitled “Video-Rate Focus Assessment”, filed concurrentlywith this application Ser. No. 60,109,960 Nov. 25, 1998, andincorporated herein by reference. The output of the focus assessment isused to control an indicator, such as the audible indicator 310. As longas the focus assessment processor 420 determines that the captured imageis not acceptable for further processing and comparison, the audibleindicator 310 is directed to emit periodic sounds to alert the user.Images are repeatedly acquired and assessed until an acceptable one isreceived. After an acceptable iris image has been received, the audibleindicator 310 is turned off and the final image is retained for furtherprocessing and comparison, for example, by the microprocessor 210, asdescribed above.

Any known technique for image focusing can be used with the imager ofthe present invention, such as those described in U.S. Pat. No.4,876,608, entitled “Focus and Signal to Noise Measurement Routines inInput Scanners”, issued to Eaton, U.S. Pat. No. 5,151,583, entitled“Focus Adjustment Device Having Restricting Means for Restricting aSelecting Action According to the Degree of Nearness of a DistanceMeasurement”, issued to Tokunaga et al., and U.S. Pat. No. 5,404,163,entitled “In-Focus Detection Method and Method and Apparatus Using theSame for Non Contact Displacement Measurement”, issued to Kubo. Thepreferred system and method for focus assessment is described below.

A focus score is computed for each video frame (i.e., each capturedimage). If the focus score exceeds a predetermined value, then it isdetermined that the image is focused enough for further processing andcomparison. If the focus score does not exceed the predetermined value,then it is determined that the image is not focused enough for furtherprocessing, and an indicator (such as indicator 310, described withrespect to FIG. 5) is activated and a further image is captured.Alternatively, a sequence of image frames can be obtained that cyclethrough a range of focus distances strobed at the video frame-rate, andthe focus score computed for each frame can enable the selection of thebest focused frame within the sequence of frames. For example, byobtaining image frames at each of several different lens settings andthen fitting a spline curve to their respective focus scores one canpredict the lens position that would deliver substantially the sharpestfocus, by setting the derivative of the parameterized spline curve tozero and then solving the equation for position.

Specific implementation features of the preferred focus assessmentsystem and method which enable its real-time operation, include (1) thecomputation of quantities in the 2D Fourier domain, without needing tocompute an actual 2D Fourier Transform of an image (this avoids the needfor approximately 2.25 million floating-point operations required for anFFT (Fast Fourier Transform) on a 500×500 pixel image, as thecomputational complexity of an FFT on n×n data is O(n²log₂n)); (2) only6,400 integer multiplications (squarings) are performed, which in turncan be eliminated altogether by using small look-up tables; (3) nofloating-point operations are required; (4) computation of focus scoresis based upon simple algebraic combinations of pixel values within localclosed neighborhoods, repeated across regions of the image; and (5)these operations not only allow the algorithm to execute in real-time,but it also enables a straightforward implementation in simple,low-cost, hardware devices that could be embedded within a digitalcamera or frame grabber.

Preferably, the focus assessment processor 420 is fast enough todetermine a focus score for each frame in a video image stream in lessthan the time it takes to acquire a new frame (e.g., approximately 25ms). The frame-by-frame focus scores can be used to control a movinglens element for rapid and accurate focus control, or alternatively, toselect which of several frames in a video stream is the one in bestfocus. The rapid selection of well-focused video frames for furtherprocessing, such as image analysis and pattern recognition, is importantin real-time computer vision because it prevents wasting processing timeon poorly-focused images.

The preferred focus assessment processor measures the focus quality ofvideo images at standard rates of 25 (PAL) or 30 (NTSC) frames persecond.

It is contemplated that the focus assessment processor 420 can beimplemented in a general purpose personal computer (PC) or by adedicated, low cost processor which is small enough to be incorporatedinto the camera electronics.

The processing of a video frame results in the return of an integervalue (on a scale between 0 and 100) reflecting the quality of focus;the larger the value of the integer, the better the focus. A value of 0indicates a completely defocused image whereas the value of 100indicates maximum focus quality. A predetermined threshold is used todetermine whether an image is sufficiently focused or whether anotherimage needs to be retrieved. For example, values greater than about 40can indicate sufficient quality of focus to warrant further imageprocessing, while values less than about 40 cause a new image frame tobe grabbed, and optional feedback provided to the focusing mechanism, ifone exists, or to the subject controlling the camera position (via theindicator 310, for example).

Optical defocus is a phenomenon of the 2D Fourier domain. An imagerepresented as a 2D function of the real plane, I(x,y), has a 2D FourierTransform F(μ,v) defamed as shown in equation 1. $\begin{matrix}{{F\left( {\mu,v} \right)} = {\frac{1}{\left( {2\pi} \right)^{2}}{\int_{x}{\int_{y}{{I\left( {x,y} \right)}^{j{({{\mu \quad x} + {vy}})}}\quad {x}\quad {y}}}}}} & (1)\end{matrix}$

In the image domain, defocus is preferably represented as convolution bythe 2D point-spread function of the defocused optics. This in turn maybe modeled as a Gaussian whose space constant is proportional to thedegree of defocus. Thus, for perfectly focused optics, the opticalpoint-spread function shrinks almost to a delta function, andconvolution with a delta function causes no change to the image.Progressively defocused optics equates to convolving with a wider andwider point-spread function, which averages together whole neighborhoodsof pixels by such a weighting function, thereby producing anincreasingly blurred image.

If the convolving optical point-spread function causing defocus ismodeled as a Gaussian whose width represents the degree of defocus, thendefocus is equivalent to multiplying the 2D Fourier Transform of aperfectly focused image with the 2D Fourier Transform of the“defocusing” (convolving) Gaussian. This latter quantity is itself justanother 2D Gaussian but in the Fourier domain, and its space constant(σ) there is the reciprocal of that of the image-domain convolvingGaussian that represented the optical point-spread function. Thepreferred focus assessment processor uses (1) the duality of convolutionand multiplication in the two domains; (2) the fact that a Gaussian hasa Fourier Transform which is itself a Gaussian, but with the reciprocalwidth because of (3) the Similarity Theorem. Thus, the 2D FourierTransform D_(σ)(μ,v) of an image defocused to degree a is related toF(μ,v), the 2D Fourier Transform of the corresponding in-focus image, asgiven by equation 2. $\begin{matrix}{{D_{\sigma}\left( {\mu,v} \right)} = {^{- {(\frac{\mu^{2} + v^{2}}{\sigma^{2}})}}{F\left( {\mu,v} \right)}}} & (2)\end{matrix}$

From the above equation, the effect of defocus is to attenuate primarilythe highest frequencies in the image, and that lower frequencycomponents are virtually unaffected by defocus since the exponentialterm approaches unity as the frequencies (μ,v) become small. Forsimplicity, the present description has assumed isotropic optics andisotropic blur, and the optical point-spread function has been describedas a Gaussian. However, the analysis can readily be generalized tonon-Gaussian and to anisotropic optical point-spread functions.

Thus, an effective way to estimate the quality of focus of an image isto measure its total amount of energy in the 2D Fourier domain at highspatial frequencies, since these are the most attenuated by defocus. Onemay also perform a kind of “contrast normalization” to make such aspectrally-based focus measure independent of image content, bycomparing the ratio of energy in the highest frequency bands to that inslightly lower frequency bands. Such spectrally-based energymeasurements are facilitated by exploiting Lord Rayleigh's theorem forconserved total power in the two domains, shown in equation 3.$\begin{matrix}{{\int_{- \infty}^{+ \infty}{\int_{- \infty}^{+ \infty}{{{I\left( {x,y} \right)}}^{2}{x}{y}}}} = {\int_{- \infty}^{+ \infty}{\int_{- \infty}^{+ \infty}{{{F\left( {\mu,v} \right)}}^{2}{\mu}{v}}}}} & (3)\end{matrix}$

Thus, high-pass filtering or band-pass filtering an image at a ring ofhigh spatial frequency (using only convolution in the 2D image domain)and measuring the residual energy, is equivalent to making thecorresponding energy measurement in the high frequency bands of the 2DFourier domain. The appropriate measurements in the 2D Fourier domain toassess focus can be performed without computing a time-consuming 2DFourier Transform. Indeed, the measurements can be performed withouteven a single floating-point operation, and even without anymultiplications if appropriate convolution kernels and look-up tablesare used.

A real-time procedure for focus assessment based on these theoreticalprinciples is used in the focus assessment processor 420. It executesmuch faster than the video frame-rate, and so real-time focusassessments can be made on a frame-by-frame basis. These can be usedeither to control the position of a focusing lens element, oralternatively as a type of autofocus system in which frames are grabbedat a variety of focal depths in order to select only the best one forprocessing, or to prevent time being wasted on processing image frameswhich are assessed to be in poor focus.

The 2D spectral measurements described above can be implemented byconvolving an image with the following convolution kernel, in whichpixel values within a predetermined region, such as, for example, an(8×8) neighborhood, are added together with the weights indicated ineach of the cells:

−1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 +3 +3 +3 +3 −1 −1−1 −1 +3 +3 +3 +3 −1 −1 −1 −1 +3 +3 +3 +3 −1 −1 −1 −1 +3 +3 +3 +3 −1 −1−1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1

It should be noted that no pixel-by-pixel multiplications are needed inorder to impose these weights. Rather, the pixels in the central regionare added together, such as the (4×4) square, that sum is tripled, andthen all pixel values in the outer two pairs of rows and columns aresubtracted from the tripled sum. The result is squared and added to anaccumulator, thus implementing the left-hand side of equation (3) abovefor this local region of the image. The complete (8×8) convolutionkernel is then moved to a new position in the image, along a samplinggrid that selects every 4th row and every 4th column, and the operationis repeated. Thus, to assess the quality of focus within the central(320×320) region of an image, this set of 64 pixel summations followedby a squaring operation is repeated a total of (320/4)²=6,400 times.

In the 2D Fourier domain, the spectral consequences of this operationcan be appreciated by examining the 2D Fourier Transform of theconvolution kernel above. The kernel is equivalent to the superpositionof two centered square box functions, one of size (8×8) and amplitude−1, and the other of size (4×4) and amplitude +4 (for the central regionin which they overlap, the two therefore sum to +3). The 2D FourierTransform of each of these square functions is a 2D “sinc” function,whose size parameters differ by a factor of two in each of thedimensions and whose amplitudes are equal but opposite, because the twocomponent boxes have equal but opposite volumes. Thus, the overallkernel has a 2D Fourier Transform K(μ,v) which is the difference of twodifferently-sized 2D sinc functions, as given by equation 4.$\begin{matrix}{{K\left( {\mu,v} \right)} = {\frac{{\sin (\mu)}{\sin (v)}}{\pi^{2}\mu \quad v} - \frac{{\sin \left( {2\mu} \right)}{\sin \left( {2v} \right)}}{4\pi^{2}\mu \quad v}}} & (4)\end{matrix}$

This is a high-pass (or ultimately a band-pass) filter, selecting only ahigh range of spatial frequencies in all orientations. Towards itscenter, corresponding to very low spatial frequencies, its valueapproaches zero (as can also be inferred from the fact that the sum ofall pixel weights in the convolution kernel shown above is zero). Thus,low frequencies play little or no role in computing a focus score, andonly relatively high frequencies contribute significantly to thecomputation of a focus score. Equation (3) shows that summing thesquares of all the local convolution sums across the image is equivalentto summing the total amount of high frequency energy in the 2D FourierTransform of the image. The action of the convolution kernel is toimpose the above power spectral weighting function so that primarilyhigh frequency energy is measured.

Finally, the summated 2D spectral energy is passed through a compressivenonlinearity of the form f(x)=100 x²/(x²+c²) in order to generate anormalized focus score in the range of 0 to 100 for any image.

The focus assessment technique is applied immediately after each imageframe is digitized and stored in the frame buffer memory 410 in order toassess whether the focus quality is sufficient to warrant any furtherprocessing. If the calculated focus quality value of the captured imageis greater than or equal to a predetermined value, the image is passedto applicable programs for further processing, for example forextraction of a biometric template. The focus assessment technique canbe used to compare the relative focus of an entire series of images inorder to select the one most in-focus (i.e. having the highest focusassessment score), as well as to measure a single image.

The focus assessment technique can be used to provide a feedbackindication to a system user who controls the position of the imagerrelative to the object being imaged. This can be accomplished byactivating an indicator which would continue, while successive imagesare captured and their focus assessed, until the focus assessment scoreexceeds a predetermined value. At this point, the indicator isdeactivated and the last image captured is transferred to the imageprocessor 210 where it is processed to extract the biometric template.

The application of the focus assessment technique in combination withthe feedback indicator helps resolve the man-machine interface problemsassociated with the use of digital imaging devices on the eye.Individuals using the system are provided positive, objective indicatorsand feedback as to the quality of image focus. The focus assessmentprocessor can also be used in any situation where it is required todetermine the quality of focus of video images at industry standardframe rates (NTSC and PAL).

Thus, the image is obtained at the imager and transmitted to an analogto digital converter 405. The digitized video information is then storedin a frame buffer memory 410. The focus assessment processor 420isolates the central 320×320 region of the image. 8×8 pixel blocks (eachpixel is in only one block) are then processed by first summing pixelsin the central 4×4 region, tripling that sum, and then subtracting fromthis value all the pixel values in the outer two pairs of rows andcolumns. This result is then squared. This process is performed on each8×8 block, and the results are summed. After the entire image has beenprocessed, the summed result is compressed nonlinearly to generate afocus score between 0 and 100. This score is then compared to apredetermined number for determining if the indicator 310 should beactivated.

The focus assessment is preferably performed by the microprocessor 210,or it can be a separate processor element within the telephone.

It is contemplated that in addition to the focus assessment processor,an auto-focus lens system could be used in the present invention. Theresults of the focus assessment control the lens system, therebyautomatically adjusting focus to produce an optimal image. This wouldplace less of a premium on the accuracy with which the user positionsthe eye, and would be helpful if the user could not see or hear theindicators described above.

The iris imager of the present invention can be used as a securitymodule for electronic devices such as a telephone. FIG. 8 is a schematicdiagram of an exemplary iris imager incorporated into a telephone inaccordance with the present invention. The imager 700 comprises thecamera 105, lens 110, mirror 120, and illuminator 130, as describedabove with respect to FIG. 1. The imager 700 also comprises visibleindicators 555, 556, 557, which are similar to indicators 305, 306, 307,respectively, described above with respect to FIG. 5. An audibleindicator 560, similar to indicator 310, is also disposed within theimager 700. The imager 700 further comprises electronics and circuitry500 for processing and comparing the obtained image. The electronics andcircuitry 500 comprises a microprocessor 510 (similar to microprocessor210) that controls the imager 700 along with an I/O controller 525 andruns software held in a ROM 505. The processor 510 is connected to theROM 505, a RAM 532 that is capable of storing at least one capturedimage or an iris, another memory 530, such as an EPROM, for storing aplurality of biometric templates or iris images that are to be comparedwith the captured iris image. The electronics and circuitry 500 is alsoconnected to the camera 105, the illuminator 130, and the indicators555, 556, 557, 560 for controlling these elements of the imager 700. Theprocessor can also comprise a focus assessment processor, similar to thefocus assessment processor 420.

It should be noted that in the embodiment of FIG. 8, the database memory530 of templates is stored within the imager 700 and not at a centralstation (as described, for example, with respect to FIG. 4), as is theprocessor 510 used in the comparison. In the embodiment of FIG. 8, thecomparison of the captured image template with the stored templatestakes place locally within the telephone, and no data is sent to thecentral station for comparison or authentication.

The imager 700 is coupled to telephone electronics 570 for transmittingencrypted or unencrypted data to another telephone or system via anantenna. The telephone electronics 570 is essentially a telephone and ispreferably a conventional cell phone having telephone electronics and isconnected to a transmission antenna. Preferably, a conventional voltageregulator (not shown) provides the appropriate operating voltage to theimager 700 from the power supply (e.g., a battery) of the phone.

Preferably, the imager 700 of the present invention is incorporated intoa handset of a telephone 575, as shown in FIG. 9. The present inventioncan be incorporated into a conventional digital cell phone, as shown inFIG. 9, such as those manufactured by Qualcomm.

FIG. 10 is a flow diagram of an exemplary method of operation of atelecommunications iris imager in accordance with the present invention.A user desiring to make a telephone call first unlocks the telephone byhaving his iris identified by the imager residing within the phone. Theeye, and thus the iris, is illuminated at step 605. An image is obtainedof the iris at step 610. At step 615, it is determined if the image issuitable for further processing and comparison, as described above. Ifthe image is not suitable, the appropriate indicators are activated atstep 620, and processing returns to step 610 with the capture of anotheriris image.

If the captured image is suitable for further processing, the image isprocessed at step 630 (an indicator can be activated to alert the userthat a suitable image has been captured) and is compared to the storedimages residing in a database, for example, in a memory, at step 635. Ifthere is no match between the captured image and the stored images, atstep 640, the appropriate indicators are activated at step 645, and theimaging routine exits. In this manner, the telephone remains locked, andcannot be used because it is determined that the user is unauthorized.

If there is a match between the captured image and the stored images, atstep 640, the phone is unlocked (and an indicator can be activated) atstep 650, and the user is then able to use the phone to place a call,for example. The phone can be returned to its locked, secure stateeither upon being powered down or upon completion of the phone call.

Although illustrated and described herein with reference to certainspecific embodiments, it will be understood by those skilled in the artthat the invention is not limited to the embodiments specificallydisclosed herein. Those skilled in the art also will appreciate thatmany other variations of the specific embodiments described herein areintended to be within the scope of the invention as defined by thefollowing claims.

What is claimed is:
 1. A telephone security module comprising: irisacquisition means having a front surface for obtaining an image of aniris of an eye; a lens having a image plane disposed in front of saidfront surface of said iris acquisition means; a mirror disposed on aside of said lens opposite said iris acquisition means; an illuminatordisposed along a side of said mirror; a memory for storing an iris imageobtained by said iris acquisition means; a processor for extracting atemplate from said stored iris image; and a communications interface fortransmitting said template to a central station.
 2. The telephonesecurity module according to claim 1, wherein said iris acquisitionmeans comprises a camera, and said mirror is a cold mirror.
 3. Thetelephone security module according to claim 2, wherein said camera issensitive to light having a wavelength in a range between about 400 nmand about 1100 nm.
 4. The telephone security module according to claim2, wherein said mirror reflects light having a wavelength in a rangebetween about 400 nm and about 700 nm and passes light having awavelength greater than about 700 nm.
 5. The telephone security moduleaccording to claim 1, wherein said illuminator emits light having awavelength in a range between about 680 nm and about 900 nm towards theiris of the eye being imaged, the eye being out of contact with the irisimaging apparatus.
 6. The telephone security module according to claim1, further comprising at least one of a visible indicator and an audibleindicator to indicate when the image of the iris has been obtained. 7.The telephone security module according to claim 6, further comprising afocus assessment processor coupled to said at least one of a visibleindicator and an audible indicator.
 8. The telephone security moduleaccording to claim 1, wherein said processor unlocks a telephoneresponsive a signal received from said central station.
 9. A system ofidentification of a person for unlocking a telephone, comprising: thetelephone security module of claim 1; a second memory for storing atleast one template of at least one image of an iris of at least oneperson's eye; and a second processor for comparing said template of saidstored iris image with said at least one stored template of said secondmemory to identify the person, and for unlocking the telephoneresponsive to the result of said comparison.
 10. The system according toclaim 9, wherein said second memory and said second processor are housedin a central station remote from the telephone security module.
 11. Thesystem according to claim 9, wherein said second processor unlocks thetelephone when said template of said stored iris image substantiallymatches said at least one stored template of said second memory.
 12. Atelephone security module comprising: iris acquisition means having afront surface for obtaining an image of an iris of an eye; a lens havinga image plane disposed in front of said front surface of said irisacquisition means; a mirror disposed on a side of said lens oppositesaid iris acquisition means; an illuminator disposed along a side ofsaid mirror; a first memory for storing at least one template of atleast one image of an iris of at least one person's eye; a second memoryfor storing an iris image obtained by said iris acquisition means; aprocessor for extracting a template from said stored iris image; and acomparator for comparing said template from stored iris image with saidat least one template to identify the person.
 13. The telephone securitymodule according to claim 12, wherein said iris acquisition meanscomprises a camera, and said mirror is a cold mirror.
 14. The telephonesecurity module according to claim 13, wherein said camera is sensitiveto light having a wavelength in a range between about 400 nm and about1100 nm.
 15. The telephone security module according to claim 13,wherein said mirror reflects light having a wavelength in a rangebetween about 400 nm and about 700 nm and passes light having awavelength greater than about 700 nm.
 16. The telephone security moduleaccording to claim 12, wherein said illuminator emits light having awavelength in a range between about 680 nm and about 900 nm towards theiris of the eye being imaged, the eye being out of contact with the irisimaging apparatus.
 17. The telephone security module according to claim12, further comprising at least one of a visible indicator and anaudible indicator to indicate when the image of the iris has beenobtained.
 18. The telephone security module according to claim 17,further comprising a focus assessment processor coupled to said at leastone of a visible indicator and an audible indicator.
 19. The telephonesecurity module according to claim 12, wherein said processor unlocks atelephone responsive to the results of said comparison.
 20. A telephonesecurity module comprising: a camera having a front surface forobtaining an image of an iris of an eye; a lens having a image planedisposed in front of said front surface of said camera; a concave coldmirror disposed on a side of said lens opposite said camera; anilluminator disposed along a side of said mirror; a memory for storingan iris image obtained by said camera; a processor for extracting atemplate from said stored iris image; and a communications interface fortransmitting said template to a central station.
 21. The telephonesecurity module according to claim 20, wherein said camera is sensitiveto light having a wavelength in a range between about 400 nm and about1100 nm.
 22. The telephone security module according to claim 20,wherein said mirror reflects light having a wavelength in a rangebetween about 400 nm and about 700 nm and passes light having awavelength greater than about 700 nm.
 23. The telephone security moduleaccording to claim 20, wherein said illuminator emits light having awavelength in a range between about 680 nm and about 900 nm towards theiris of the eye being imaged, the eye being out of contact with the irisimaging apparatus.
 24. The telephone security module according to claim20, further comprising at least one of a visible indicator and anaudible indicator to indicate when the image of the iris has beenobtained.
 25. The telephone security module according to claim 24,further comprising a focus assessment processor coupled to said at leastone of a visible indicator and an audible indicator.
 26. The telephonesecurity module according to claim 20, wherein said processor unlocks atelephone responsive a signal received from said central station.
 27. Atelephone security module comprising: a camera having a front surfacefor obtaining an image of an iris of an eye; a lens having a image planedisposed in front of said front surface of said camera; a concave coldmirror disposed on a side of said lens opposite said camera; anilluminator disposed along a side of said mirror; a first memory forstoring at least one template of at least one image of an iris of atleast one person's eye; a second memory for storing an iris imageobtained by said camera; a processor for extracting a template from saidstored iris image; and a comparator for comparing said template fromstored iris image with said at least one template to identify theperson.
 28. The telephone security module according to claim 27, whereinsaid camera is sensitive to light having a wavelength in a range betweenabout 400 nm and about 1100 nm.
 29. The telephone security moduleaccording to claim 27, wherein said mirror reflects light having awavelength in a range between about 400 nm and about 700 nm and passeslight having a wavelength greater than about 700 nm.
 30. The telephonesecurity module according to claim 27, wherein said illuminator emitslight having a wavelength in a range between about 680 nm and about 900nm towards the iris of the eye being imaged, the eye being out ofcontact with the iris imaging apparatus.
 31. The telephone securitymodule according to claim 27, further comprising at least one of avisible indicator and an audible indicator to indicate when the image ofthe iris has been obtained.
 32. The telephone security module accordingto claim 31, further comprising a focus assessment processor coupled tosaid at least one of a visible indicator and an audible indicator. 33.The telephone security module according to claim 27, wherein saidprocessor unlocks a telephone responsive to the results of saidcomparison.